Shiny - Can dynamically generated buttons act as trigger for an event

Question

I have a shiny code that generates actions buttons from a numericInput and each of those actions buttons generate a plot when clicked using a observeEvent. The problem is that I don't know how to trigger an event with dynamically generated buttons. The workaround I used was to make a observeEvent for each button but if I generate more buttons than the obserEvents I created it won't work.

library(shiny)
library(shinydashboard)


ui <- dashboardPage(
  dashboardHeader(title = "Dynamic selectInput"),
  dashboardSidebar(
    sidebarMenu(
      menuItemOutput("menuitem")
    )
  ),
  dashboardBody(
    numericInput("go_btns_quant","Number of GO buttons",value = 1,min = 1,max = 10),
uiOutput("go_buttons"),
plotOutput("plot")
  )
)

server <- function(input, output, session) {
  output$menuitem <- renderMenu({
    menuItem("Menu item", icon = icon("calendar"))
  })


  output$go_buttons <- renderUI({
    buttons <- as.list(1:input$go_btns_quant)
    buttons <- lapply(buttons, function(i)
      fluidRow(
      actionButton(paste0("go_btn",i),paste("Go",i))
      )
    )
  })

  #Can this observeEvents be triggerd dynamicly?
  observeEvent(input[[paste0("go_btn",1)]],{output$plot <-renderPlot({hist(rnorm(100,4,1),breaks = 10)})})
  observeEvent(input[[paste0("go_btn",2)]],{output$plot <- renderPlot({hist(rnorm(100,4,1),breaks = 50)})})
  observeEvent(input[[paste0("go_btn",3)]],{output$plot <- renderPlot({hist(rnorm(100,4,1),breaks = 100)})})
  observeEvent(input[[paste0("go_btn",4)]],{output$plot <- renderPlot({hist(rnorm(100,4,1),breaks = 200)})})
  observeEvent(input[[paste0("go_btn",5)]],{output$plot <- renderPlot({hist(rnorm(100,4,1),breaks = 500)})})

}

shinyApp(ui, server)

Answer 1

You can also create observers dynamically. Just make sure that they are created only once, otherwise they will execute several times.

Below is your code modified to create as many observers as buttons. Please note that if an observer for the button already exist, it should not be created. You can customize your observers too, so each observer could have its own behavior.

library(shiny)
library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(title = "Dynamic selectInput"),
  dashboardSidebar(
    sidebarMenu(
      menuItemOutput("menuitem")
    )
  ),
  dashboardBody(
    numericInput("go_btns_quant","Number of GO buttons",value = 1,min = 1,max = 10),
uiOutput("go_buttons"),
plotOutput("plot")
  )
)

server <- function(input, output, session) {
  output$menuitem <- renderMenu({
    menuItem("Menu item", icon = icon("calendar"))
  })

  # to store observers and make sure only once is created per button
  obsList <- list()

  output$go_buttons <- renderUI({
    buttons <- as.list(1:input$go_btns_quant)
    buttons <- lapply(buttons, function(i)
      {
        btName <- paste0("go_btn",i)
        # creates an observer only if it doesn't already exists
        if (is.null(obsList[[btName]])) {
          # make sure to use <<- to update global variable obsList
          obsList[[btName]] <<- observeEvent(input[[btName]], {
            cat("Button ", i, "\n")
            output$plot <-renderPlot({hist(rnorm(100, 4, 1),breaks = 50*i)})
          })
        }
        fluidRow(
          actionButton(btName,paste("Go",i))
        )
      }
    )
  })

}